Conventional liquid beverages are distributed in disposable containers with all of the ingredients of the beverage pre-mixed with the liquid beverage inside the container. The liquid is either pasteurized or contains preservatives to prevent degradation of ingredients that are suspended or dissolved in the liquid. Any additional ingredients that are not be pre-mixed with the liquid prior to distribution but that are designed to be added to the liquid before consumption are conventionally kept separate from the liquid in a second container. Keeping additional ingredients separate from the liquid in a second container is inconvenient for the consumer, who must then add the additional ingredients from the second container into the container holding the liquid. Also, the consumer must accurately measure and combine the ingredients, because variations in the ratio of additional ingredients to liquid may alter the properties (e.g., taste, viscosity, organoleptic properties, etc.) of the final beverage.
Disposable containers typically include a cap designed to provide a leak-resistant seal over the opening of the container containing the liquid, for example, over the mouth of a bottle. A cap that could contain additional ingredients separate from the liquid while allowing the user to add the additional ingredients to the liquid and still provide a leak-resistant seal would be desirable.